In a known lightning arrester system for a wind turbine a gap in the lightning down-conductor between the rotor blade and the nacelle—two parts which are rotatable relative to each other—is bridged by spark gaps, as described in DE 4436197 A1. However, rotor blades of wind turbines will not only be hit by lightning, but may also be subjected to electric charging due the static electricity caused by friction with the air flowing along the blades' surface. Accordingly, US 2003/170122 A1 proposed that a connection to ground is provided in parallel to the spark gaps to enable continuous electric discharging of the blades.
In other types of lightning arrester systems, sliding contacts are used instead of spark gaps, as described in WO 2005/050008 A1. U.S. Pat. No. 7,390,169 B2, FIG. 4, pertains to another arrester system of that type in which a spark gap member is arranged adjacent to and in parallel with a sliding contact in order to prevent the sliding contact from being damaged by lightning. The sliding contact and the spark gap member are mounted commonly in a mounting plate with spacers between the mounting plate and a contact face.